This invention relates generally to magnetic disk data storage systems, and more particularly to magnetic write transducers and methods of making same.
Magnetic disk drives are used to store and retrieve data for digital electronic apparatuses such as computers. In FIGS. 1A and 1B, a magnetic disk data storage systems 10 of the prior art includes a sealed enclosure 12, a disk drive motor 14, a magnetic disk 16, supported for rotation by a drive spindle S1 of motor 14, an actuator 18 and an arm 20 attached to an actuator spindle S2 of actuator 18. A suspension 22 is coupled at one end to the arm 20, and at its other end to a read/write head or transducer 24. The transducer 24 (which will be described in greater detail with reference to FIG. 2A) typically includes an inductive write element with a sensor read element. As the motor 14 rotates the magnetic disk 16, as indicated by the arrow R, an air bearing is formed under the transducer 24 causing it to lift slightly off of the surface of the magnetic disk 16, or, as it is termed in the art, to xe2x80x9cflyxe2x80x9d above the magnetic disk 16. Alternatively, some transducers, known as xe2x80x9ccontact heads,xe2x80x9d ride on the disk surface. Various magnetic xe2x80x9ctracksxe2x80x9d of information can be written to and/or read from the magnetic disk 16 as the actuator 18 causes the transducer 24 to pivot in a short arc as indicated by the arrows P. The design and manufacture of magnetic disk data storage systems is well known to those skilled in the art.
FIG. 2A depicts a magnetic read/write head 24 including a substrate 25 above which a read element 26 and a write element 28 are disposed. Edges of the read element 26 and write element 28 also define an air bearing surface ABS, in a plane 29, which can be aligned to face the surface of the magnetic disk 16 (see FIGS. 1A and 1B). The read element 26 includes a first shield 30, an intermediate layer 32, which functions as a second shield, and a read sensor 34 that is located within a dielectric medium 35 between the first shield 30 and the second shield 32. The most common type of read sensor 34 used in the read/write head 24 is the magnetoresistive (AMR or GMR) sensor which is used to detect magnetic field signals from a magnetic medium through changing resistance in the read sensor.
The write element 28 is typically an inductive write element which includes the intermediate layer 32, which functions as a first pole, and a second pole 38 disposed above the first pole 32. The first pole 32 and the second pole 38 are attached to each other by a backgap portion 40, with these three elements collectively forming a yoke 41. The combination of a first pole tip portion 43 and a second pole tip portion 45 near the ABS are sometimes referred to as the yoke tip portion 46. A write gap 36 is formed between the first and second poles 32, 38 in the yoke tip portion 46. The write gap 36 is filled with a non-magnetic electrically insulating material that forms a write gap material layer 37. This non-magnetic material can be either integral with (as is shown here) or separate from a first insulation layer 47 that lies below the second yoke 38 and extends from the yoke tip portion 46 to the backgap portion 40.
Also included in write element 28 is a conductive coil 48, formed of multiple winds 49 which each have a wind height Hw. The coil 48 can be characterized by a dimension sometimes referred to as the wind pitch P, which is the distance from one coil wind front edge to the next coil wind front edge, as shown in FIG. 2A. As is shown, the wind pitch P is defined by the sum of the wind thickness Tw and the separation between adjacent winds Sw. The conductive coil 48 is positioned within a coil insulation layer 50 that lies above the first insulation layer 47. The first insulation layer 47 thereby electrically insulates the coil layer from the first pole 32, while the coil insulation layer 50 electrically insulates the winds 49 from each other and from the second pole 38.
The configuration of the conductive coil 48 can be better understood with reference to a plan view of the read/write head 24 shown in FIG. 2B taken along line 2Bxe2x80x942B of FIG. 2A. Because the conductive coil extends beyond the first and second poles, insulation may be needed beneath, as well as above, the conductive coil to electrically insulate the conductive coil from other structures. For example, as shown in FIG. 2C, a view taken along line 2Cxe2x80x942C of FIG. 2A, a buildup insulation layer 52 can be formed adjacent the first pole, and under the conductive coil layer 48. As is well known to those skilled in the art, these elements operate to magnetically write data on a magnetic medium such as a magnetic disk 16 (see Figs. 1A and 1B).
More specifically, an inductive write head such as that shown in FIGS. 2A-2C operates by passing a writing current through the conductive coil layer 48. Because of the magnetic properties of the yoke 41, a magnetic flux is induced in the first and second poles 32, 38 by write currents passed through the coil layer 48. The write gap 36 allows the magnetic flux to fringe out from the yoke 41 (thus forming a fringing gap field) and to cross a magnetic recording medium that is placed near the ABS. A critical parameter of a magnetic write element is a track width of the write element, which defines track density. For example, a narrower track width can result in a higher magnetic recording density. The track width is defined by geometries in the yoke tip portion 46 (see FIG. 2A) at the ABS. These geometries can be better understood with reference to FIG. 2C. As can be seen from this view, the first and second poles 32, 38 can have different widths W1, W2 respectively in the yoke tip portion 46 (see FIG. 2A). In the shown configuration, the track width of the write element 28 is defined by the width W2 of the second pole 38. The gap field of the write element can be affected by the throat height TH, which is measured from the ABS to the zero throat ZT, as shown in FIG. 2A. Thus, accurate definition of the track width and throat height is critical during the fabrication of the write element.
Another parameter of the write element is the number of winds 49 in the coil layer 48, which determines magnetic motive force (MMF) of a write element. With increasing number of winds 49 between the first and second poles 32, 38, the fringing field is stronger and, thus, the write performance increases. The number of winds is limited by the yoke length YL, shown in FIG. 2A, and the pitch P between adjacent winds 49. However, to obtain faster recording speeds, and therefore higher data transfer rates, it may be desirable to have a shorter yoke length YL because this can shorten the flux rise time. This relationship can be seen in the graph of yoke length YL versus flux rise time shown in FIG. 2D. Therefore, to maximize the number of coil winds while maintaining fast write speeds, it is desirable to minimize the pitch P in design of write elements.
However, the control of track width, throat height, and coil pitch can be limited by typical fabrication processes, an example of which is shown in the process diagram of FIG. 3. The method 54 includes providing a first pole with first and second edges in operation 56. This operation can include, for example, forming a plating dam, plating, and then removing the dam. In operation 58, a write gap material layer is formed over the first pole. In particular, the write gap material layer is formed over an upper surface and the first and second edges of the first pole. Also, in operation 58, a via is formed through the write gap material layer to the first pole in the backgap portion 40 (see FIG. 2A). In the instance herein described, the write gap material layer extends above the first pole in the area between the yoke tip portion and the backgap portion, although in other cases the write gap material layer may not be above this area. A buildup insulation layer is also formed in operation 60, adjacent the first and second edges, with the write gap material layer between the first pole and the buildup insulation layer. The buildup insulation layer is typically formed by depositing (e.g., spinning) and patterning photoresistive material and then hard baking the remaining photoresistive material. Such processes often result in the height of the buildup insulation layer being non-uniform and different than the height of the write gap material layer, as is illustrated in FIGS. 2A and 2C.
The method 54 also includes forming a first coil layer above the write gap material layer and the buildup insulation layer in operation 62. This can include first depositing a seed layer above the first pole. Typically, photoresistive material can then be deposited and patterned. With the patterned photoresistive material in place, conductive material can be plated. With removal of the photoresistive material, the remaining conductive material thereby forms the first coil layer.
Unfortunately, when there is a difference in height between the write gap material layer and the buildup insulation layer, the patterning of the photoresistive material for the first coil layer can be complicated. In particular, it can be difficult to pattern the various heights to have consistent geometries. More specifically, winds of the resulting first coil layer can be wider at lower levels than at higher levels, such as between the first and second poles. Thus, for a given pitch, such greater width at the lower levels can result in smaller distances between winds. This can, in turn, result in electrical shorting between winds which can be detrimental to the write element performance. To avoid such electrical shorting, the minimum wind pitch can be set to a desired value that will result in adequate yield of non-shorting conductive coil layers. Because the coil winds are more narrow between the first and second poles, the resulting pitch there is typically greater than, and limited by this minimum. For example, typical wind pitches between the first and second poles may be limited to no less than about 3 microns. For a given number of winds and wind thickness, this in turn limits the minimum yoke length, and thereby limits the data transfer rate and data density as described above. For example, a pitch of about 3 microns may be adequate for recording densities on the order of about 2 Gb/sq.in., however, these typical pitches can be inadequate for larger recording densities, such as about 10 Gb/sq.in.
In operation 64, the method 54 further includes forming a coil insulation layer above the first coil layer that is formed in operation 62. In addition, a second pole is formed above the coil insulation layer of operation 64, in operation 66.
Still another parameter of the write element is the stack height SH, the distance between the top surface of the first pole 32 and the top of the second pole 38, as shown in FIG. 2A. Of course, this height is affected by the thickness of the first insulation layer 47, the thickness of the coil layer 48 and any other coil layers that might be included, and the height of the coil insulation layer 50 and any other coil insulation layers that might be included. The stack height can be an indicator of the apex angle xcex1, which partially characterizes the topology over which the second pole must be formed near the yoke tip portion. Typically, the reliability of the write element decreases as the apex angle xcex1 increases. This is due, at least in part, to the corresponding increased difficulty, particularly in the yoke tip portion 46, of forming the second pole 38 over the higher topography of the stack. For example, the definition of the second pole width W, shown in FIG. 2C, including photoresist deposition and etching, can be decreasingly reliable and precise with increasing topography. When demand for higher density writing capabilities drives yoke tip portions to have smaller widths W, this aspect of fabrication becomes increasingly problematic.
Greater track width control can be attempted using other processes such as focused ion beam (FIB) milling, however such processes can be expensive. To support higher data transfer rate applications, the second pole can otherwise be formed by lamination, which can be more time consuming than without lamination. Alternatively, the track width can be defined by the first pole width W1. However, such processes can also be expensive, complex, and result in lower production yields.
Also, with higher topography, when the second pole is formed, for example by sputtering or plating, the material properties of the second pole in the sloped region, adjacent the second pole tip region 45, can be undesirable. Thus, this decreased reliability results in undesirable lower production yield.
As will be appreciated from the above, the performance of a write head is limited by manufacturing limitations such as minimum coil pitch and stack height limitations. Therefore, methods are needed to increase the magnetic performance of a write head in spite of these manufacturing limitations. One possible method of increasing the magnetic performance of a write head in spite of the manufacturing limitations described above is to use very highly magnetic materials such as Ni45Fe55 in the construction of the poles. However such materials, being highly corrosive present their own manufacturing challenges. For example, the high temperatures required to cure the insulation layer deposited on the coil causes such highly magnetic materials to corrode. Therefore there remains a need for a magnetic read write head which takes advantage of the magnetic performance properties of high Bsat materials while addressing the corrosion problems inherent in such materials.
The present invention is embodied in a write head having first and second poles which together join to form a yoke. The first pole has respective write gap and back gap pedestals extending from its top surface at its front and back ends. The pedestals are constructed of a high Bsat material such as Ni45Fe55 which greatly enhances the magnetic properties of the yoke by promoting efficient magnetic flux concentration in the write gap portion at the front of the yoke. The write head is produced by a process whereby the pedestals are covered with a write gap material during cure of a subsequently deposited insulation layer. The write gap material is then removed from the back gap pedestal, exposing a surface of the back gap pedestal for contact with the second pole. Covering the pedestals with the write gap material protects the pedestals from corrosion during the high temperature cure of the insulation layer.
More particularly, the space surrounding the pedestals on top of the first pole is covered with a dielectric layer which is planarized by a chemical mechanical polishing process to create a smooth flat surface across the top of the dielectric layer as well as the tops of the pedestals. Upon this planarized surface of the dielectric layer the coil is formed. First, a copper seed layer is deposited. Then a copper coil is deposited onto the seed by a photolithographic plating process. The coil is provided with a pair of contacts for supplying electrical current to the coil. After the coil has been deposited, the seed is removed by an etching process.
With the coil formed on the dielectric layer and the seed removed, the layer of write gap material in the form of SiO2 is deposited over the dielectric layer and coil as well as the top of both pedestals. By depositing the write gap material on top of the coil rather than beneath it, the thickness of the write gap material can be more closely controlled. This is because the write gap material will not be attacked by the etching process used to remove the seed layer which was deposited in order to form the coil.
The insulation layer is then deposited on top of the coil. In order to ensure that the insulation will adhere to the write gap material a very thin layer of HMDS is first deposited onto the write gap material. The insulation layer is then deposited as a photoresist which is spun onto the coil and masked to provide vias over the pedestals and coil contacts. The insulation is also masked to provide vias over the coil contacts. This is followed by a cure process which involves subjecting the insulation layer to high temperatures. Using SiO2 as the write gap material advantageously causes the cured insulation to have a smooth gradual slope at its front end adjacent the write gap pedestal.
After the insulation has been cured, the write gap material can be locally removed at the locations of the back gap pedestal and the contacts for coil and sensor leads. This is accomplished by an etching process such as a reactive ion etch or ion beam etch. Keeping the high Bsat pedestals covered with write gap material during the high temperature cure of the insulation layer prevents corrosion of the pedestals. The write gap material can then be locally removed to expose the back gap pedestal without significantly effecting the back gap pedestal. Thus the corrosion problem inherent in using high Bsat materials in the poles of a write head is efficiently overcome.
A second pole is then formed on top of the insulation layer and over the write gap material in the write gap portion at the front of the first pole. The second pole contacts the exposed top of the back gap pedestal, whereby the first and second poles together form the yoke. As will be appreciated by those skilled in the art, the smooth slope of the insulation layer will cause the second pole to define a low apex angle, contributing to the magnetic performance and reliability of the write head. The second pole can also be constructed of Ni80Fe20, which can be deposited by conventional plating processes, or alternatively can be constructed of high Bsat materials such as Ni45Fe55 deposited by a plating process. The use of sputter deposited high Bsat materials is made possible by the low apex angle provided by the present invention.
As will be appreciated the present invention provides a write head which can take advantage of the excellent magnetic properties of high Bsat materials while solving the corrosion problems inherent in such materials. Also, the present invention provides improved control of write gap thickness as well as reduced apex angle. These and other advantages of the present invention will become apparent to those skilled in the art upon a reading of the following descriptions of the invention and a study of the several figures of the drawings.